SUMMARY/ABSTRACT A major obstacle to HIV eradication is the presence of infected cells that persist despite suppressive antiretroviral therapy (ART). HIV largely resides outside of the peripheral circulation, and thus, numerous anatomical and lymphoid compartments that have the capacity to harbor HIV are inaccessible to routine sampling. Novel, non-invasive, in vivo methods are urgently needed to address this fundamental gap in knowledge. We recently completed the pre-clinical development, animal testing, and first-in-human PET- magnetic resonance (MR) imaging studies of 89Zr-VRC01. In a pilot feasibility study of 15 participants, we observed significantly increased 89Zr-VRC01 uptake in various lymphoid and other tissues in HIV-infected individuals with detectable viremia and on suppressive ART compared to uninfected controls. Importantly, PET tracer uptake in inguinal lymph nodes in viremic and ART-suppressed participants who underwent lymph node sampling significantly and positively correlated with HIV protein expression measured directly in cells. These exciting data suggest the PET imaging of the HIV reservoir has the potential to advance the field of HIV curative strategies. Our goals are to determine the anatomical location and temporal dynamics of HIV infection in viremic and ART-suppressed individuals and validate the tracer uptake with true measures of HIV infection. We will study location and dynamics before and after ART and during a separately funded, highly monitored treatment interruption protocol which will begin enrolling during the first year of our proposed study. Throughout these studies, we will simultaneously measure the reservoir directly (using lymph node and gut samples) and compare these tissue assessments of the HIV reservoir to the total 89Zr-VRC01 uptake by PET-MR imaging. We have established close collaborations with the EXPLORER imaging program at UC Davis. This unique PET technology has the highest sensitivity of any existing human scanner which will likely prove to be critically important in imaging HIV reservoirs among individuals on long-term ART. We recently completed EXPLORER imaging in two HIV-infected individuals and show dramatic increases in image resolution and signal/noise ratios. We hypothesize that PET-MR imaging using 89Zr-VRC01 in conjunction with the EXPLORER platform will provide a quantifiable, non-invasive measure of tissue-wide reservoirs and will identify anatomical foci of HIV recrudescence. Our aims are to: (1a) quantify 89Zr-VRC01 PET activity in HIV-infected participants (ART- suppressed, HIV controller, viremic) and matched uninfected controls, (1b) compare 89Zr-VRC01 uptake before and after initiation of ART, and (1c) determine the correlation between PET signal and tissue measures of HIV burden, (2) determine if the ultra-sensitive EXPLORER platform will increase the ability of 89Zr-VRC01 PET imaging to detect persistent HIV in ART-suppressed individuals, and, (3) determine the anatomical foci of HIV recrudescence during ATI using the 89Zr-VRC01 PET, PET-MR, and EXPLORER platforms.